Question about sound of 737 NG engines (heard from flight deck)
 

Hello everyone. I am currently editing a existing soundpack for PMDG 737 NG (addon program for Flight Simulator 9) and wondering about following:
When the engine spool up (in start phase, when starter is active) and pass approx. 10-12 % N1, a load bass sound is observed. Does this sound orign from the engine or from resonans in a/c body?
When on crz, and the engine throttle is moved to IDLE and N1 pass app 65 % a bass sound is again heard. Does this sound come every time when passing approx this % N1, or is this a little bit variating from a/c to a/c? I mean I never have heard this bass resonance sound when spooling up engine, (under T/O situation). It really seems to only appear when spooling down to IDLE on crz. Anybody who can explain a little bit about these sound I have heard when I have been observer / visitor on flight deck?
Then I would have been very thanksfull!
A little promo of my soundwork (currently still under progress) can be heard here: http://www.home.no/nv31/737NGpromo.mp3
regards

I would recommend posting this in the Tech Log forum mate as it's quite specific about sounds during flight. Perhaps a pilot would have more experience of this..

Cheers

Thank you for tip